In chemical and biomedical research and development, it is common to manipulate large numbers (e.g., thousands) of fluid containers which must be readily and automatably opened and closed, and yet must also be stored for months or years. The need to open and close the containers readily tends to induce the use of relatively poorly sealed containers, whereas the desire to store the containers for months or years tends to make it desirable to achieve tight sealing, for example to avoid evaporation loss and contamination from the outside.
The fluid containers used in chemical and biomedical research are subject to substantial chemical compatibility constraints, for example that they should not be made of materials which would be attacked by the solvents which they are designed to hold. Such constraints will also apply to the closures of such fluid containers. Adhesives are generally not preferred for closure of such fluid containers because of concerns about contamination and nonuniformity arising from adhesive residue left over from one closure to the next.
Examples of fluid containers widely used in chemical and biomedical research and development are well plates and micro tubes. Well plates are commonly used which have 96, 384, and 1536 wells, although other numbers of wells are also in use. The dimensions and other characteristics of well plates have been standardized by the Society for Biomolecular Screening. A common size of well plate is 127.76 by 85.48 by 14.35 mm. Well plates are commonly designed to be stacked on top of each other in storage. Microtubes are commonly used in racks of 96 or 384. These racks of microtubes conform to dimensions similar to the length and width of well plates so they can be handled by similar robotic and automation equipment.
For well plates, a wide variety of lids have been developed. An example of a well plate lid of the prior art is described in U.S. Patent Application Publication No. 2003/0108450. That well plate lid uses the weight of the lid to provide the force which holds the lid to the well plate. The lid is stated to weigh 400 g preferably. A compliant sealing member, preferably of silicone rubber, forms part of the lid and is pressed against the well plate.
There have also been efforts in the art to adapt to evaporation losses. In particular, in some cases the outer wells of a well plate are not used to hold fluids of interest but instead are filled with a volume of the solvent in which those fluids are stored. This solvent in the outer wells has been observed to reduce the rate at which the solvent in the inner wells evaporates. The outer wells are sometimes referred to as “moat wells” when so used.
An alternative means to adapt to evaporation losses is to periodically audit the fluid levels in the reservoirs of the container and to add solvent to those reservoirs as needed. U.S. Pat. No. 6,932,097 describes a convenient automatable way of carrying out the auditing by means of focused acoustic energy. A variety of patent applications to the present assignee describe generally the process of acoustic ejection as employed in chemical and biomedical research, for example U.S. Pat. Nos. 6,416,164 and 6,612,686.
The assignee of the present application has previously filed U.S. Patent Application Publication No. 2006/0201948, which disclosed an approach to dealing with evaporation losses which involves the use of closures which contain reservoirs for additional fluid. Such closures are effective in reducing the loss from evaporation.
U.S. patent application Ser. No. 11/698,004 (U.S. Patent Application Publication No. 2007/0175897), also assigned to the assignee of the present invention, discloses a further approach to dealing with evaporation losses through closure design.
When well plates are supplied with an appropriate closure, they may be stored for considerable periods of time, at least on the order of months, without a damaging loss of fluid in the wells themselves. However, the purpose of storing fluids in well plates is generally to at least occasionally remove fluid for testing purposes. The process of removing fluid is often carried out by means of acoustic ejection.
The removal of fluid from a well plate generally implies removing the well plate's closure. The closure may remain off for a considerable time if fluid is removed from multiple wells in the well plate. It is possible to remove quite small quantities of fluid and use them in tests, for example quantities on the order of picoliters. In such a context it is quite possible that the evaporation losses caused by the removal of the closure to be comparable to or exceed the fluid removed for purposes of experimentation.
There is still a need to provide well plate closures which are further effective in dealing with evaporation losses and in particular losses that occur when fluid samples are removed from a well plate.